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Reliability of Confocal Choroidal Laser Doppler Flowmetry

From the University Eye Clinic, Basel, Switzerland.

PURPOSE. To assess the variability in choroidal laser Doppler flowmetry (LDF).

METHODS. Five measurements of choroidal blood flow were obtained on 5 days in both eyes of 10 subjects. Reliability, sensitivity, and sample size calculations were performed. Yield, the intensity of the returning light (direct current [DC]) divided by the signal amplification (gain) used during recording, was calculated (yield = DC/gain). The correlation between yield and the LDF parameters velocity, volume, and flux was analyzed. Reliability, sensitivity, and sample size calculations were repeated after correcting for this relationship. The influence of different light-scattering properties on the returning signal was assessed in a model eye.

RESULTS. Yield and the LDF parameters, velocity, volume, and flux, correlated significantly in a regression model. After the influence of yield was partialized out, reliability, reproducibility, sensitivity, and statistical power improved markedly. The high reliability of yield in a given eye (87%) suggests, that, besides varying recording settings on different days, individual specific scattering properties within the eye influence LDF measurements. Comparison of model eye data with human data disclosed a low signal-to-noise ratio with decreasing yield. Correcting for yield did not affect the sensitivity to blood flow changes induced by hypercapnia or a suction cup.

CONCLUSIONS. Tissue-scattering properties alter the characteristics of the returning light, and recording settings affect the outcome of the analysis of the returning light during LDF measurements. Partializing out the influence of yield markedly improves the reproducibility of choroidal LDF.

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